Storing the maximum amount of data on the minimum amount of media and reading and writing data on the media at a maximum rate are goals of the data processing industry. Magnetic tape is commonly used as the media because it is inexpensive and provides significant data storage capacity per unit volume. Improvements in magnetic recording have increased the track and bit recording density for magnetic tape thereby maximizing the number of bits stored per square inch of tape. Further improvements in the recording density of magnetic tape are increasingly difficult to attain due to the need for accurate alignment of the tape with the read/write head to read the data written on the tape from data tracks of the tape. Any misalignment of the data tracks of the magnetic tape with the read/write head causes errors in the data read from and written to the tape.
Using both sides of magnetic tape doubles the data storage capacity of the tape. Two sided (double sided) tape recording has been disclosed in U.S. Pat. No. 5,293,285, which is hereby incorporated by reference.
Two situations need to be considered for two sided tape recording. The first situation is reading and writing on only one side of the magnetic tape at a time. The second situation is reading and writing on both sides of the magnetic tape simultaneously.
In the first situation, data tracks having data blocks are on only one side of the magnetic tape. Thus, the symmetry of the data blocks on both sides of the magnetic tape is not required. In the second situation, data tracks having data blocks are on both sides of the magnetic tape. As a result, the symmetry of data blocks on both sides of the magnetic tape is required for data integrity and data search. In essence, the data blocks must be read from and written to both sides of the tape in a proper order to ensure that the data is usable.
For the second situation, prior art apparatus and methods for two sided recording generally employ a pair of read/write heads. One of the pair of read/write heads is positioned on one side of the magnetic tape and the other one of the pair of read/write heads is positioned on the other side of the tape. Reading from and writing to both sides of the magnetic tape simultaneously with the pair of read/write heads doubles the data transfer rate.
A problem with prior art two sided recording apparatus and methods for the second situation is that the read/write heads must be synchronized properly with each other. This means that the read/write heads must be turned on and off at the same time so that data is written to and read from both sides of the tape in the proper order. Thus, when one read/write head is reading and writing part of a data block at a predetermined area on one side of the tape the other read/write head must be reading and writing the other part of the data block on a corresponding predetermined area on the other side of the tape. In essence, read/write head synchronization means that the pair of read/write heads are performing corresponding actions on corresponding positions of both sides of the tape simultaneously.
Synchronization affects the symmetry of the data blocks on both sides of the magnetic tape. When the read/write heads are not synchronized, reading and writing of part of a data block on one side of the tape is either too fast or too slow as compared to the reading and writing of the other part of the data block on the other side of the tape. This violates the symmetry of the data blocks and data integrity is not preserved.
What is needed is a tape drive and method for reading and writing on double sided tape with a pair of synchronized read/write heads.